drm/i915/icl: Fix clockgating issue when using scalers

drm/i915/icl: Fix clockgating issue when using scalers

Fixes the clock-gating issue when pipe scaling is enabled.
(Lineage #2006604312)

V2: Fix typo in headline(Chris)
    Handle the non double buffered nature of the register(Ville)
V3: Fix checkpatch warning. BAT failure for V2 on gen3 looks unrelated.
V4: Split the icl and skl wa's(Ville)
V5: Split the checks for icl and skl(Ville)
V6: Correct the flipped checks in intel_pre_plane_update(Ville)
V7: Use enum for pipe and extend the WA for plane scalers(Ville)
V8: Eliminate the redundant use of pch_pfit(Ville)

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Clint Taylor <clinton.a.taylor@intel.com>
Cc: Aditya Swarup <aditya.swarup@intel.com>
Signed-off-by: Radhakrishna Sripada <radhakrishna.sripada@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190417185901.14833-1-radhakrishna.sripada@intel.com